Control rheostat unit



June 18, 1940. Q o. H. HASSELBAUM CONTROL RHEOSTAT UNIT Filed Sept. 7, 1938 2 Sheets-Sheet 1 Patented June 18, 1940 UNITED STATES PATENT OFFICE CONTROL BHEOSTAT UNIT Application September 7, 1938, Serial No. 228,783

8 Claims. (CL 201-48) This invention relates to a control rheostat together with an indicating lamp therefor, and more particularly for use as the control unit for small motors, such as an automobile heater motor.

An object of this invention is to produce such a control rheostat with a novel switch structure.

Another object is to provide such an element in which the control resistance is to have substantial heat transfer with the switch element.

Another object is to provide a structure in which the control resistance is provided with free circulation of air for cooling the same.

Another object is to provide a protective structure around said resistance to prevent grounding displacement or any distortion of said resistance.

Another object is to provide an arrangement in which the indicating lamp is illuminated at its maximum brilliancy for all positions of control.

A further object is to provide such a structure incorporating a fuse interposed between the switch and the battery.

A still further object is to provide a novel mounting for the indicating lamp in the foregoing structure.

An additional object is to provide a control device of the above kind for controlling a plurality of operating elements together with the indicating lamp.

The foregoing and other objects of my invention will be best understood from the following description of exempliflcations thereof, reference being had to the accompanying'drawings, wherein:

Fig. l is a top View of the control unit with the switch and lamp assembly removed there-- from, wherein there is also shown diagrammatically a circuit with which the control unit may be used;

Fig. 2 is a back view of the control unit shown in Fig. 1;

Fig. 3 is an end view of the control unit viewed from the bottom of Fig. 2;

Fig. 4 is an end view of the control unit together with the switch arm and indicating lamp assembly in place thereon as viewed from the top of Fig. 1;

Fig. 5 is a view of the switch arm and lamp socket unit;

Fig. 6 is a bottom view of the unit shown in Fig.

Fig. '7 is an enlarged cross-section of theswitch arm and lamp assembly taken along line 1-4 of Fig. 8;

Fig. 8 is a top view of the assembled device showing the various positions of control;

Fig. 9 is a view similar to Fig. 1 of another embodiment of my invention;

Fig. 10 is a. back view of the control unit shown in Fig. 9;

Fig. 11 is an end view of the control unit viewed from the bottom of Fig. 9;

Fig. 12 is an end view of the control unit together with the switch arm and indicating lamp assembly in place thereon,- as viewed from the top of Fig. 9;

Fig. 13 is an enlarged cross-sectional view of the switch arm and lamp assembly taken along the line l3--|3 of Fig. 15;

Fig. 1-1 is a bottom view of the unit shown in Fig. 13;

Fig. 15 is a top view of the assembled modification of Fig. 9 showing the various positions of control;

Fig. 16 is a side view of the casing shown in Fig. 13 with part of the wall broken away to show the internal construction; and

Fig. 17 is a plan view of the detent spring of the switch structure.

In the drawings, I represents an insulating body made of ceramic material or other suitable refractory insulation. The body I is provided at one end thereof with two square holes 2 extending through said body. In each of theholes 2 is mounted a coil 3 of resistance wire. Due to the fact that the holes 2 are square and the coils 3 are round, sufiicient space-is left between the walls of the holes 2 and the sides of the coils 3, through which air may freely circulate, thus providing cooling of the coils 3. The two coils 3 are connected in series by means of a loop 4 on the back of the body I. The loop is secured in place and electrically connected to a conducting pin 5 extending through the insulating body to the front thereof, where it is provided with a contact head 5'. The two outer ends 6-6 of the two coils 3 are connected respectively to two pins 1 and 8 likewise through the insulating body i. The coil ends 8-6 thus are securely retained in place on the body I. The insulating body is recessed to receive the loop 5 and the ends 6. Also the coils 3 are shorter than the length of the holes 2. In this way the insulating body I forms a protective structure around the resistance to prevent any undesired conductive elements from coming into contact with the resistance to ground it or in any other way disturb the electrical connections. The resistance is thus also mechanically protected against displacement or injuring. The ends of the pins 1 and 8 at the front of the insulating body I are provided with contact heads 1' and 8, respectively. A conducting strip 9 at the back of the body I is connected to the pin 1 and extends to the side of the body where it supports a binding terminal I8, whereby an external electrical connection may be made. A plate II of suitable conducting material is mounted on the front of the insulating body I, and is retained in place thereon by means of a pin or rivet I2 extending through the body I. In order to prevent any rotation of the plate I I, tongues I 2a formed on the plate II extend into corresponding recesses in the body I. An arcuate contact strip Ila is supported adjacent the upper edge of the plate II by two pins I8 and I4 extending through the body I. The tops of the pins I8 and I4 in the face of the strip IIa are recessed so as toprovide detents engaging a corresponding projection on the switch arm 21, to be described below. In order to provide additional positioning detent depressions, the plate II is provided with an additional depression I5, and the contact strip IIa with an additional depression I50. At the back of the body I, the pin I4 supports a spring clip fuse holder I6. A similar spring clip fuse holder I1 is supported at the bottom of the body I by means of a pin I8 extending through projection I8 formed on said body I. The spring clip I1 is also provided with a binding terminal 28, whereby another external electrical connection may be made to the control unit. A i'use 2|, indicated in dotted lines, may be supported at the two ends thereof by the spring clips I8 and I1.

The typical circuit shown in Fig. 1 may consist of a battery 22, one terminal thereof being connected to the binding terminal N by means of a conductor 23; the other terminal of the battery 22 may be grounded at 24. The element to be controlled by the mechanism may be a motor 25 which may be the heater motor in an automobile, a moving picture projector or the like. One terminal of this motor is connected by means of the conductor 25' to the binding terminal III, the other terminal of the motor being grounded at 26. The switch arm 21, indicated in dotted lines in Fig. 1, is adapted to overlie the switch plate II and the various contacts associated therewith. As will be described in more detail below, an indicating lamp 28 is directly connected to the switch arm 21 through an electrical connection 25. The opposite side of the lamp is grounded at 30.

The switch arm 21, which is shown most clearly in Fig. 7, is provided at its central portion with a relatively elongated slot 31 which fits around a sleeve 3i. The slot 31 is made elongated to permit a certain amount of rock or play of the switch arm 21, but is shaped to prevent relative rotation between the switch arm and shaft. The rocking is such as to insure at all times a good contact with the switch plate I I and the various contacts associated therewith. A spring 32 biases the switch arm 21 to the outer end of the sleeve 3!, which sleeve is in turn provided with a stop 33 to retain the switch arm in place thereon. The switch arm 21 is bent so as to provide two contact legs 34 and 35 at the opposite ends thereof. ()ne of these legs, for example the leg 35, is provided with a projection. 36 which is adapted to fit into the various detent indentations on the contacts ii, as described above. An insulating plate 38 is retained in place on the sleeve M by being clamped between a head 39 formed at the inner end oi the sleeve II and a clamping shoulder 88a swedged from the sleeve 8| onto the upper face of the plate 88. The sleeve 8| is hollow and receives therein the head 48 of a contact rod 4I extending through the insulating plate 88 and the head 88. In order to bias the contact rod 4I to the outer position, a spring 42 is contained within the hollow sleeve 8|.

The insulating plate 88 also carries a lamp socket sleeve 48 which is mounted thereon by means of lugs 44 extending through openings in the insulating plate 88; The sleeve 48 is of the type which retains a lamp thereon by means of bayonet slots cooperating with bayonet pins on the lamp base. The sleeve 48 has these bayonet slots formed therein in a novel manner. At each of four equally-spaced points around the sleeve 48, tongues 45 are cut into the side walls of the sleeve 48 and indented inwardly. Each tongue is provided with an elongated leg 46 and a shorter leg 41 between which is located a recess 48 to receive the bayonet pin 48, mounted on the base ll of a cooperating lamp 28. The lamp 28 is provided with the usual center contact 52 which directly engages the contact rod 4I. Due to the presence of the four equally-spaced long legs 48, the base III is accurately centered within the sleeve 48.

The usual lamp 28 is provided with two diametrically-opposed bayonet pins. As will be noted, the socket sleeve 43 is, however, provided with four bayonet slots. By this construction it is unnecessary to orientate the lamp in any particular position in order that it may be inserted in the socket in the proper position. Due to the particular construction described above, it is merely necessary to insert the lamp 28 in any position, whereupon the pins'48 will be guided between the long leg 46 of one tongue and the short leg 41 of the adjacent tongue. Thereupon the lamp can only be rotated in a direction in which the pins 43 will ride over the tops of the two short legs 41 immediately adjacent said pins. Upon releasing the lamp 28, the spring 42 acting upon the contact rod M will push the pins 49 firmly into position in the recesses 48. Such a construction greatly facilitates the insertion of the lamp in the proper position.

The control unit is also provided with a translucent head 53 formed of glass, plastic, or other translucent material. The head 53 is provided with a thinned portion 54 at the end thereof in order to permit light radiated from the lamp 28 to pass more readily through the head 53 at that point, thus providing a brighter spot at the center of said translucent head. In order to retain the head 53 in position on the structure, the sleeve 43 is provided with an elongated slot 55 at one side in the head thereof. The head 53 is provided with a cooperating elongated tongue or feather 56 on one side of the inner wall thereof. The sleeve 43 on the wall directly opposite said slot 55 is provided with a projection 51 which is adapted to fit into a corresponding depression (not shown) on the inner wall of the head 53. In order to retain the head 53 in place, it 'is merely necessary to slide it over the sleeve 43 so that the feather 56 slides into the slot 55, whereupon the projection 51 will snap into the corresponding depression in the head 53, thus retaining it in the proper position on the sleeve 43.

A mounting sleeve 58 surrounds the sleeve 43 in such a way that said sleeve 43 freely rotates within the mounting sleeve 58. Non-rotatably carried by the sleeve 58 is a casing 59 which is adapted to cover the switching structure of the control unit. The casing 58 is provided with three tongues 60, each ending with a. tab 8|. I The body I is provided with three cooperating recesses 62 in the edges thereof. The casing 59 is inserted on the body I so that the tongues 80 fit into the corresponding recesses 02. The tabs 61 are then bent over onto the back face of the body I, in this way retaining the casing 59 together with the switch arm and lamp socket unit mounting arm. Such a mounting arm is usually a grounded portion of the automobile frame, and

thus the casing of the control element is at ground potential.

provided with an indicating arrow, represented by the solid arrow 66 in Fig. 8.

When the structure described above is connected in the circuit, as shown in Fig. 1, and the head 53 is rotated to the off position, the switch arm 21 will occupy the position indicated by the dotted lines in Fig. 1. In order to prevent rotation of the switch arm 21 beyond this off position in the wrong direction, the plate II is pro-' vided with an upstanding stop 65. Since the battery is connected to the terminal 20, which in turn is connected through the fuse 2I to the contact IIa through the pin I4, the circuit terminates at this point inasmuch as the switch arm does not engage thecontact Ila. Thus, neither the motor 25 nor the lamp 20 is energized. As the head 53 is rotated so as to swing the switch arm 21 in a clockwise position around the pin I2 in Fig. l, the leg 34 of the switch arm 21 will come into contact with the contact head 1, while the projection 36 will snap into the recessin the contact Heat the pin 14. Under these conditions, a circuit is completed from the battery through the conductor 23, binding terminal 20, spring clip I1, fuse 2I, spring clip I6, pin I4, contact IIa, switch arm 21, contact 1', pin 1, strip 9, binding terminal I0, conductor 25', motor 25, ground 26, and ground 24 back to the battery 22. In this way the motor 25 is connected directly across the battery 22, and therefore operates at its maximum or high speed. It will be noted that the fuse H is included in this circuit, and thus protects the motor 25 against overload as well as protecting the switch against accidental short-circuits. A circuit is also established for the lamp 28 which is identical with that established for the motor 25 up to the contact arm 21. However, from there the circuit for the lamp 20 continues through the sleeve 3i, the contact rod 41, the lamp terminal 52 through the lamp itself to the base contact 50, the socket sleeve 43 which is grounded, and back through the ground connection 24 to the battery 22. Under these conditions the lamp 28 likewise is connected directly across the battery 22, and is illuminated to its maximum brilliancy. If the switch arm 21 is rotated further in the same direction by means of the head 53, the leg 34 will contact the terminal 5' and the projection 36 on the leg 35 will snap into the depression I5a on the contact IIa.

. will be decreased to its medium value.

In order to indicate the various positions of the switch, the head 53 may be,

Under these conditions the circuit remains the same except for the fact that the resistance coil 3 on the right-hand side of Fig. 1 is now connected in the motor circuit previously traced. Due to this series resistance, the motor speed 25 Since, however, the lamp is still connected directly across the battery 22, its illumination remains unchanged. As the switch arm 21 is rotated further, the leg 34 will come into contact with the contact 8 and the projection 36 will snap into the depression on the contact IIa adjacent the pin I3. Under these conditions, the circuit is altered merely by the interposition of the resistance of 'bothcoils 3 in the motor circuit traced above. Under these conditions the additional resistance will slow the speed of the motor down to its low value, but the illumination of the lamp 28 will remain unchanged. It will be noted that further rotation of the switch arm 21 will likewise be prevented by the stop 65. In each of the positions of operation, as indicated above, the projection 36 snaps into a corresponding depression at I3, I4, I5 or I5a. the switch arm 21, and can readily be felt by the operator so that he has no difficulty in locating the switch arm 21 in exactly the proper position. The projection 36 in its corresponding depression likewise prevents shifting of the switch arm 21 from any position in which it is placed, due to vibration or jarring.

Heretofore, in controls of this type, great difflculty has been experienced in damage to the switching structure, due to the heating of the switch structure by the control resistances. I have eliminated this difficulty in my present structure by locating the resistances 3 out of any appreciable heat transfer relation to the'switch structure itself, and by providing the air cooling referred to above. This has permitted the utilization of relatively complicated switch structures for accomplishing various types of control, of which the present application is one example. Other types of control which this arrangement makes possible are exemplified in my application entitled Control rheostat switch structure, filed simultaneously herewith.

Another embodiment of my invention is shown in Figs. 9 to 17, inclusive, in which, in addition to a heater motor, a control is afforded for an additional operating element, such as. for ex ample, a defrosting motor within the automobile. In these figures, IOI represents a flat insulating body made of ceramic material. or other suitable refractory insulation. The body IN is provided at one end thereof with two square holes I02 extending throu h the body. In each of the holes I02 is mounted a coil I03 of resistance wire. in the case of Fig. l, the difference in shape between the holes I02 and the resistance coils I03 affords ample circulation of cooling air around the coils I03. The tWo coils I03 are connected in series by means of a loop I0 1 on the back of the body IN. The loop is secured in place and electrically connected to a conducting pin I05 extending through the insulating body to the front thereof where it is provided with a contact head I05. The two .outer ends I06-I05 of the two coils I03 are connected respectively to two pins I01 and I08 likewise extending through the insulating body. The ends of the pins I01 and I08 at the front of the insulating body are provided with contact heads I01 and I08, respectively. A conducting strip I09 at the front of the body IOI connects the contact I01 to an adjacent contact 0' which is mounted upon a pin IIO extending through the body Ill and supporting a binding terminal III upon the rear face of said insulating body. By means of the binding terminal III, an external electrical connection may be made to a battery I20, for example. Adjacent the contacts heretofore described is located a conducting switch plate III which is secured on the front face of the insulating body IOI by means of a pin or rivet II3 extending through the body IOI and supporting a binding terminal I I4 on the rear face of said insulating body. By means of the binding terminal II4, an external electrical connection may be made from the switch plate to a controlled member, such as, for example, a heater motor I23. In order to prevent the switch plate II! from being displaced on the body IOI, it is provided with a tongue II5 projecting into a recess in the face of the body "II.

In order to provide for the control of an additional operating member, the switch plate H2 is cut away at a predetermined portion II6. In the space left by this cut-away portion is mounted a contact ii? carried by a pin II1 extending through the insulating body I01. supports on the rear face of the body IOI another binding terminal IIB to which anaccessory, such as, for example, a defrosting motor I26 may be electrically connected. The switch plate I I 2 may be provided with a plurality of contact positions IIS.

A typical circuit, such as shown in Fig. 9, may consist of the battery I 20 connected from one terminal thereof by a conductor I2I to the binding terminal H8, and thus to the contact H0. The other end of the battery I20 may be grounded at I22. The heater motor I23 may be connected from one terminal thereof by the conductor I24 to the binding terminal H4, and thus to the switch plate H2. The motor I23 may likewise be grounded at I25. The accessory motor I23 may be connected from one terminal thereof by a conductor I21 to the binding terminal III, and thus to the contact III. The accessory motor I26 also may be grounded at I28. An indicating lamp I29 is in constant electrical connection I30 with a switch arm I3I which is adapted to overlie switch plate H2 and the various contacts associated therewith, as will be more fully described below. The opposite side of the lamp may be grounded at I32.

The switch arm I3 I, which is shown most clearly in Fig. 13, consists of two portions, 8. straight contact arm I33 and an offset contact arm I34. The offset arm 134 is provided with an offset portion I35 which underlies a portion of the arm I33. .Both contact arms are slipped over and supported on a conducting sleeve I36. For this purpose the contact arm I33 is provided with a slot I31, and the offset portion I35 of the contact arm I34 is likewise provided with a similar slot. These slots are suiilciently large to provide for a relative rocking motion between the contact arms and the sleeve I 36; but are shaped to prevent relative rotation. In order to retain the contact arms on the sleeve I36, a stop member I30 is provided at the outer end of said sleeve. The contact arms are biased to the outer end of the sleeve I36 by means of a compression spring I30. The offset portion I35 is provided with a fulcrum projection I40 which bears against the lower face of the contact arm I33. is provided with a contact portion I which is adapted to engage the switch plate H2 at the The pin H1 The contact I34" contact positions II! as well as the contact 1'. The contact arm I33 is provided on its short end with an auxiliary contact projection I33.

The sleeve I36 carrying the associated switch arm structure is mounted on an insulating plate I42 in a manner similar to that described in connection with Fig. 7. Likewise the insulating plate I42 carries a lamp socket sleeve I43. The insulating plate I42 also carries a center contact rod I44 electrically connected to the sleeve I36, and thus to the switch arm unit I3I. As above described, the lamp socket sleeve I43 is provided with a plurality of bayonet-recessed tongues I45. The lamp I29 is adapted to be received within the socket sleeve I43 and retained in place thereon by means of the bayonet-recessed tongues I45. This modification is also supplied with a translucent head I46 similar to the head 53 of the previous modification.

Around the socket sleeve I43 is supported a mounting sleeve I41 within which the socket sleeve I43 can turn freely. The mounting sleeve I4! is similar to the mounting sleeve 53 in Fig. l and supports a casing I48. The casing I48 is provided with a plurality of tongues I49 which are adapted to fit into corresponding recesses I5I in the body MI. The tongues I49 are also provided with end tabs I50 which are adapted to be bent over upon the rear face of the body IM to retain the casing and its associated structure in place on said body. In order to provide a positioning mechanism, the edge of the insulating plate I42 is provided with a plurality of detent notches I53. These notches are adapted to cooperate with a resilient detent spring I54 carried by the casing I40. The spring I54 is provided with a projecting central detent portion I55 which is adapted to be received in each of the notches I53 to resiliently retain the switch in a predetermined position of operation. The detent spring I54 is supported in place in the casing I48 by means of two openings I56 formed in the opposite side walls of the casing I48. A tongue I51 on each end of the detent spring I54 snaps into a corresponding opening I56, and thus retains the spring I54 in place. In order to prevent the spring I54 from bending at its detent projection I55, it is provided with two thinned portions I58 on opposite sides 'of said projection I55. In order to give to the operator an audible click upon the rotation of the switch into a predetermined position, the length of the spring I54 between the two tongues I51 is made slightly shorter than the distance between the inner side walls of the casing I 48. Under these conditions such an audible click is produced. In order to provide stops to prevent the rotation of the switch beyond its off position or its low-speed position, the insulating plate I42 is cut away along an edge I53 to provide two shoulders I60 at opposite ends of said cut-away portions. A detent stop I6I is formed in the casing I 40 by slotting and indenting the upper side wall thereof. The stop I3I cooperates with the shoulders I60 to limit the rotation of the switch to the proper degree.

' When the switch arm is located in the position indicated by the dotted lines in Fig. 9, no contact is made by said switch arm with either the contact I 01 or the contact H0, and thus the battery I 20 is not connected in the circuit. In this position the elements associated with the control unit are deenergized, and thus this constitutes the oil. position of the control unit. As the switch arm unit I3I is rotated in a clockwise direction, the switch arm I33 comes first into engagement with the contact III! while the switch arm I34 rides onto the contact III, the projection I4I snapping into the recess in the face of said contact. Under these conditions the battery I is connected through the switch arm unit I3I to the contact 1', and thus energizes the accessory motorI23. The pressure of the contact arm I33 against the contact III' working through the fulcrum I forces the projection I33 of the arm I33 into contact with the underlying portion of the switch plate II2. Thus the motor I23 beingconnected to the plate H2 is also energized at its maximum. speed. It will be noted that due to the fulcrum arrangement, the two contact surfaces of the arm I33 are always forced into simultaneous, good contact with the underlying contact surfaces. The lamp I23 being directly electrically connected to the switch arm unit I3I will be energized to its full brilliancy. As the switch arm unit I3I is shifted clockwise to the next position, the switch arm I33 will engage the contact I01 while the switch arm I34 will engage the switch plate II2, the projection I snapping into a corresponding recess I53 on the plate I42. Since the contact H1 is not engaged in this position, the accessory motor I26 is thereupon deenergized and remains deenergized in the subsequent positons of the control unit. However, the heater motor I23 being directly electrically connected to the switch plate H2 is now connected to the battery I2I, due to the electrical connection, and established by the switch arm assembly I3I. It will be noted that neither of the resistance coils I03 are connected in series with the motor I23, and thus this heater motor will be operated at its maximum or high speed. In the subsequent operations of the switch arm unit, the resistance coils I03 are successively connected in series with the motor I23, substantially as described in connection with Fig. 1, and thus the motor is actuated at its medium and low speed, respectively. However, since the lamp I23 is directly in parallel with the motor I23 in each position of the switch, the intensity of luminosity of the lamp I29 will be decreased in accordance with the decrease in speed of the'heater motor I23.

The two-piece construction of the switch arm unit I3I accomplishes other valuable results. Due to the arrangement of the various switch contacts, it is important that each of the contact arms I33 and I34 shall have a good electrical connection with its associated contact in each position of the switch. If but a one-piece switch arm were used, the biasing spring I39 might exert its pressure in connection with one of the contact arms, but the pressure on the other switch arm might be insufficient toestablish the desired good electrical connection. Due, however, to the fulcrum relationship afforded by the protection I40 bearing against the switch arm I33 and the relative rocking motions, possible pressure exerted by the spring I33 against the offset portion ofthe switch arm I35 must necessarily be exerted both upon the switch arm I33 and the switch arm I34. This arrangement, therefore, insures that good electrical contact is made with each of the contacts in each position of the switch arm control unit. Due to the fact that the switch unit is advanced in substantial heat transfer relation with respect to the resistance coils I03, none of the heat energized by said coils I03 can reach the switch structure so as to cause any damage thereto.

Of course it is to be understood that the present invention is not limited to the particular details of construction as described above, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A control rheostat comprising a body of refractory insulating material having substantially parallel upper and lower faces, the thickness of said body between said faces being substantially less than the maximum dimension of said faces, an opening extending substantially at right angles to said faces and entirely through said body at a predetermined position thereon, a coil of resistance wire with its axis substantially perpendicular to saidfaces mounted in said opening, said opening and coil being of such shape as to provide an open space through which cooling air may circulate around said coil through said opening, a plurality of switch contacts mounted on said body on one of said faces displaced substantially from said coil and connected to spaced points on said coil, and a movable switch arm overlying and movable into various contact positions with said contacts, said contacts and switch arm being out of substantial heat transfer relation with respect to said coil.

2. A control rheostat comprising a fiat body of refractory insulating material, two openings extending entirely through said body at predetermined positions thereon, a coil of resistance wire mounted in each of said openings, said openings and coils being of such shape as to provide an open space through which cooling air may circulate around said coils through said openings, said coils being connected in series by a conductor electrically connected to a contact pin mounted on said body, the ends of said coils being connected to two additional contact pins also mounted on said body adjacent said first contact pin, a conducting switch plate mounted on said body adjacent said contacts, a movable switch arm adapted to make successive electrical contacts between said switch plate and said contacts, said contacts and switcharm being out of substantial heat transfer relation with respect to said coil.

3. A switch comprising a flat body of refractory insulating material, a plurality of contacts supported on said body, a switch arm assembly adapted to overlie said contacts and to successively connect pairs of said contacts together, an actuating shaft supported adjacent said contacts and carrying said switch arm assembly, said switch arm assembly comprising a pair of contact arms each carried on said actuating shaft, adapted to move along said shaft and perform a limited rocking motion with respect thereto, said two contact arms extending on opposite sides of said shaft, one of said contact arms being provided with an offset portion underlying said other contact arm, said offset portion being provided with a fulcrum projection bearing against the lower face of said other contact arm on the side of said shaft from which said other contact arm projects, and spring means for biasing said contact arms to the outer end of said shaft into engagement with said contacts.

4. Aswitch comprising a flat body of refractory insulating material, a plurality of contacts supported on said body, a switch arm assembly adapted to overlie said contacts and to successively connect pairs of said contacts together, an actuating shaft supported adjacent said contacts and carrying said switch arm assembly, said switch arm assembly comprising a pair of contact arms each carried on said actuating shaft, adapted to move along said shaft and perform a limited rocking motion with respect thereto, said two contact arms extending on opposite sides of said shaft, one of said contact arms being provided with an offset portion underlying said other contact am, said offset portion being provided with a fulcrum projection bearing against the lower face of said other contact arm on the side of said shaft from which said other contact arm projects, said other contact arm having an auxiliary contact surface projecting on the opposite side of said shaft, said contacts being disposed on said body to provide contact surfaces to be engaged by said contact arms andauxiliary contact surface during each position of said switch, and spring means for biasing said contact arms to the outer end of said shaft into engagement with said contacts.

5. A control rheostat comprising a body of refractory insulating material having substantially parallel upper and lower faces, the thickness of said body between said faces being substantially less than the maximumdimension of said faces,an opening extending substantially at right angles to said faces and entirely through said body at a predetermined position thereon, a coil of resistance wire with its axis substantially perpendicular to said faces mounted in said opening, said opening and coil being of such shape a: o provide an open space through which cooling air may circulate around said coil through said opening, a plurality of switch contacts mounted on said body on one of said faces displaced substantially from said coil and connected to spaced points on said coil, and a movable switch arm overlying and movable into various contact positions with said contacts, said contacts and switch arm being out of substantial heat transfer relation with respect to said coil, said insulating body projecting beyond said resistance wire on all sides thereof to prevent accidental touching or displacement of said resistance wire.

6. A control rheostat comprising a body of refractory insulating material having substantially parallel upper and lower faces, the thickness of said body between said faces being substantially less than the maximum dimension of said faces, an opening extending substantially at right angles to said faces and entirely through said body at a predetermined position thereon, a coil of resistance wire with its axis substantially perpendicular to said faces mounted in said opening, said opening and coil being of such shape as to provide an open space through which cooling air may circulate around said coil through said opening, a plurality of switch contacts mounted on said body on one of said faces displaced substantially from said coil and connected to spaced points on said coil, and a movable switch arm overlying and movable into various contact positions with said contacts, a plate movable with and secured to said switch arm, a plurality of detent depressions in the edge of said plate, and a spring detent mounted on said insulating body and adapted to engage each of said depressions in various positions of operation of said switch arm. 7. A control rheostat comprising a body of refractory insulating material having substantially parallel upper and lower faces, the thickness of said body between said faces being substantially less than the maximum dimension of said faces, an opening extending substantially at right ang es to said faces and entirely through said body at a predetermined position thereon, a coil of resistance wire with its axis substantially perpensaid faces mounted in said opening, said opening and coil being of such shape as to provide an open space through which cooling air may circulate around said coil through said Opening, a plurality of switch contacts mounted on said body on one of said faca displaced substantially from said coil and connected to spaced points on said coil, and a movable switch arm overlying and movable into various contact positions with said contacts, a plate movable with and secured to said switch arm, a plurality of detent depressions in the edge of said plate, a spring detent mounted on said insulating body and adapted to engage each of said depressions in various positions of operation of said switch arm, said plate being cut away along one edge to provide a pair of shoulders, and a stop mounted on said insulating plate to engage said shoulders in limiting positions of said switch arm.

8. A control rheostat comprising a body of refractory insulating material having substantially parallel upper and lower faces, the thickness of said body between said faces being substantially less than the maximum dimension of said faces, an opening extending substantially at right angles to said face and entirely through said body at a predetermined position thereon, a coil of resistance wire mounted in said opening, said opening and coil being of such shape as to provide an open space through which cooling air may circulate around said coil through said opening, a plurality of switch contacts mounted on said body on one of said faces displaced substantially from said coil and connected to spaced points on said coil, and a movable switch arm overlying and movable into various contact posi tions with said contacts, said contacts being out of substantial heat transfer relation with respect to said coil.

OSCAR H. HASSELBAUM. 

